1. Field of the Invention
The present invention relates to a circularly-polarized-light-extracting optical element for use in a display such as a liquid crystal display. More particularly, the present invention relates to a process of producing a circularly-polarized-light-extracting optical element including a layer having a cholesteric structure (hereinafter referred to as a “cholesteric layer”), to such a circularly-polarized-light-extracting optical element, to a polarized-light-emitting device including the optical element, and to a liquid crystal display including the optical element.
2. Description of Related Art
A circularly-polarized-light-extracting optical element including a cholesteric liquid crystal layer has conventionally been known as an optical element for separating incident light into right-handed and left-handed polarized components and selectively reflecting or transmitting these circularly polarized components. In order to more efficiently utilize a component of light circularly polarized in a predetermined direction (right- or left-handed circularly polarized light) by such a circularly-polarized-light-extracting optical element, it has been demanded to improve the circularly-polarized-light-extracting optical element so that it can extract right- or left-handed circularly polarized light of wavelength in a wider wave range. To meet this demand, there has been proposed a circularly-polarized-light-extracting optical element composed of a laminate of a plurality of cholesteric liquid crystal layers with different chiral pitches (Japanese Laid-Open Patent Publications No. 271731/1996 and No. 264907/1999). Further, a polarized-light-emitting device including such a circularly-polarized-light-extracting optical element, and a liquid crystal display including the same have been proposed as well (Japanese Laid-Open Patent Publication No. 304770/1997).
If the above-described circularly-polarized-light-extracting optical element is used for a display such as a liquid crystal display, it is essential that the condition of polarization be uniform throughout the surface of the circularly-polarized-light-extracting optical element. In a liquid crystal display or the like, a circularly-polarized-light-extracting optical element 10 is, as shown in FIG. 8, placed between polarizing plates 31 and 32 such as linear or elliptical polarizers that are arranged in the cross nicol disposition (in such a disposition that the axes of transmission of the two polarizing plates cross at a right angle); and the displaying state of the display changes with the state of a liquid crystal cell (not shown in the figure) sandwiched between the polarizing plates 31 and 32. The above liquid crystal display is designed so that the polarizing plates 31 and 32 can completely shield incident light to prevent light leakage when the liquid crystal cell (not shown in the figure) is in such a state that it fully transmits polarized light.
However, it has been found the following fact: since the condition of polarization is not uniform throughout the surface of a circularly-polarized-light-extracting optical element 10 incorporated in a practical display, bright and dark stripes appear on the screen of the display even in the case where polarizing plates 31 and 32 are expected to fully shield incident light; and the displaying quality of the display is thus drastically lowered.